1. Field of the Invention
The present invention relates to an alternating current (AC) detection circuit applicable to a power supply such as that of a plasma display panel (PDP), and more particularly, to an AC detection circuit for power supply, which is configured to detect an AC using a comparing part such as a shunt regulator, and a transistor.
2. Description of the Related Art
In general, a switching mode power supply (SMOS) applicable to a plasma display panel (PDP) TV set employs a sequence circuit so as to protect a PDP driving board. In order to employ such a sequence circuit, an alternating current (AC) detection circuit detecting AC input is required, as well as a brownout circuit blocking the sequence circuit when a low voltage is inputted.
An AC detection signal outputted from an AC detection circuit is commonly created in a direct current (DC) waveform and a square waveform, according to an AC signal's forms.
In an AC detection circuit employing the DC waveform, a sequence circuit is controlled and a brownout circuit is configured by using a Zener diode and a transistor.
Like this, a configuration using the Zener diode and the transistor uses an excessive resistance value in an input port so as to reduce influences of standby power consumption and embody the operation characteristics of the sequence circuit and the brownout circuit, thereby causing circuit design review (CDR) problems in the case of the Zener diode and the transistor. Also, there are many required components, so the problem of cost is encountered.
The following descriptions are of circuits detecting an AC voltage using a Zener diode according to the related art. An AC detection circuit employing a DC waveform is configured to be active high by using a transistor, a Zener diode, and a photodiode. Such a circuit uses approximately twenty-seven components.
This circuit is configured to perform the conversion of an AC voltage to a DC voltage using a first Zener diode and a capacitor such as a ceramic capacitor or a film capacitor, allowing a current to flow through a second Zener diode when the converted voltage is higher than a breakdown voltage in the second Zener diode, causing the current to operate a transistor, and generating an AC detection signal accordingly.
Since such an AC detection circuit according to the related art uses the Zener diode and the transistor, a complex circuit configuration is required for a bias and the protection of the Zener diode from surges. This causes an increase in the number of components, resulting in an increase in the area required for the increased components and a production cost.